In a manner of speaking, seeing how we are all material (even our souls) compared to God. Even angels are not immaterial in the most extreme sense. However, this present world will pass away, and there will be a bodily resurrection, but our bodies will be transfigured.

Because they're our bodies. They're part of us. A significant and substantial part. Would you also ask why we keep our souls if they're going to be transfigured?

They become worm and other parasite food when we die.

Is the soul formless?

I get it by your "transfigured" that you mean spiritualised in saying that the world will pass away.Or am I wrong? Is the material world, the Universe we see and live with planets stars and Galaxies forever/eternal?

What is the purpose of a bodily resurrection if our bodies will be transfigured anyway?

God created mankind with body and soul, that is how he intends us to exist. Our current fallen nature and the world around us is subject death, decay, and self-destruction. This is not fitting for creation, brought from non-existence into being, to revert from being to non-existence. The point of the general resurrection is to bring everything out of its state of corruption, death, and decay into a state of incorruption, life, and passing from glory to glory.